Method for reducing surface cracking in extruded plastic material

ABSTRACT

Method for end-shaping blanks of soap cut from extruded logs preliminary to die box pressing by subjecting the cut end surfaces of the blanks to transverse shear in order to bend and compress the flow lines at the cut ends exposed and opened by segmenting the extruded log, the transverse shear being provided by forcing the soap blank through an opening defined by spaced apart die surfaces separated by less than the longitudinal length of the soap blank, the die surfaces being rounded at the soap blank receiving edge and tapering divergently from the soap blank receiving edge.

Feb. 26, 1974 BENGTSQN ETAL 3,794,709

METHOD FOR REDUCING SURFACE CRACKING IN EXTRUDED PLASTIC MATERIAL 2 Sheets-Sheet 1 ERIC 6. BENGTSON LYNN H. LANDER Er; i: 5. i I? Filed Feb. 12, 1971 INVENTORS ATTORNEYS Feb. 26, 1974 BENGTSQN EIAL 3,794,709

mug FOR REDUCING summon cmcxme EXTRUDED FLA TIC MATERIAL Flled Feb. 12, 1971 S 2 Sheets-Shet s ERIC G. BENGTSON LYNN 'H. LAN DER INVENTORS NEYS United States Patent 3,794,709 METHOD FOR REDUCING SURFACE CRACKING IN EXTRUDED PLASTIC MATERIAL Eric G. Bengtson, Cluster, and Lynn H. Lander, Ridgefield, N.J., assignors to Lever Brothers Company, New

York, NY.

Filed Feb. 12, 1971, Ser. No. 114,945 Int. Cl. C11d 13/14, 13/28 U.S. Cl. 264-323 1 Claim ABSTRACT OF THE DISCLOSURE Method for end-shaping blanks of soap cut from extruded logs preliminary to die box pressing by subjecting the cut end surfaces of the blanks to transverse shear in order to bend and compress the flow lines at the cut ends exposed and opened by segmenting the extruded log, the transverse shear being provided by forcing the soap blank through an opening defined by spaced apart die surfaces separated by less than the longitudinal length of the soap blank, the die surfaces being rounded at the soap blank receiving edge and tapering divergently from the soap blank receiving edge.

BACKGROUND OF THE INVENTION This invention relates to the field of plastic extrusion and more particularly to a method and apparatus for preparing detergent and/or soap blanks for stamping into finished bars or tablets by which surface cracking of the soap bars is reduced.

It has long been the practice to extrude plastic materials such as soaps and detergents in a continuous log; the extrusion causes the plastic material to flow in laminar layers. After extrusion the log is usually cut into blanks for further processing, the blanks being the same size as or slightly larger than the finished soap bars. In forming the blanks the soap log is cut by means of wires or knives and the laminar flow lines at the surfaces of severance are opened. These opened flow lines are the principal cause of surface cracking in the soap bars during use.

Several methods have been suggested for soap bar trimming and reworking. U.S. Pat. No. 2,413,995 is directed to a bar trimmer in which the soap blank is shaped by means of sharp edged rigid knives which successively engage and trim or plane away the surface portion of the soap bar to give the soap bar the cross-sectional shape corresponding closely to the cross-sectional shape of the cake of soap finally to be produced. Soap finishing in this manner reduces flow line cracks in the finished surface but the tendency to surface cracking reappears as the fin ished surface is worn off during use. In U.S. Pat. No. 2,465,398 a soap trimmer is disclosed in which the soap blanks are moved along a conveyor belt in the direction of the axis of the extrusion. At a preset point each blank is moved in a lateral direction off the conveyor belt to a set of cutter blades or dies which trim the blank to a shape approximately that of the die box. Patentees deal only with shaping and trimming soap; elimination or reduction of surface cracking is neither taught nor inherent in the apparatus disclosed.

SUMMARY OF THE INVENTION In the method of the present invention plastic material such as a milled soap is formed into a log by extrusion. The extruded log is then transported by means of a conveyor belt along a path, typically parallel to the axis of extrusion. As the log proceeds, it is cut by means of wires or knives into appropriately sized blanks each having one or more opened surfaces of severance along which the blank was separated from the log. The blanks continue on the conveyor belt until they reach a stop. The blanks are then laterally pushed off the conveyor belt and forced through a reworking die with rounded edges which subjects each opened surface of severance of the blank to shear and compression to bend and compress the open fiow lines in order to eliminate surface cracking in the blank. Thus each cut surface of the blank is reworked simultaneously'by the die which remains rigid. The reworking is accomplished not by cutting but by high transverse shear and compression created on the cut surfaces of the blank.

An alternate method may be used wherein a log of plastic material is used rather than blanks so that the log is continuously reworked in the dies.

The object of the present invention is to provide a means of bending the flow lines perpendicular to their normal direction and compressing them thus sealing the opened surfaces of the blank. In this way the reworking die will substantially reduce or eliminate both the surface cracking and substratum surface cracking when the bar is used.

The essential part of the invention is the die with rigid blunt surfaces. The die can be either stationary or mobile. The leading edge of the bearing surface of the die has a small radius of curvature producing a smooth bending and compressing effect. The die then angles back to increase the cross-sectional area thus relieving the pressure on the blank and facilitating its removal. The die may take either of two forms: (1) the die may function separately or (2) the die may be affixed to or be an integral part of the press die box.

Accordingly the invention comprises an apparatus for end-shaping blanks of plastic material such as milled soap or the like cut from extruded logs preliminary to die box pressing. The apparatus includes dies adapted to receive and contact the cut end surfaces of the soap blanks, the dies having a pair of spaced apart opposite ends defining an opening, the spaced apart ends having die surfaces separated by less than the longitudinal length of said soap blanks, and the die surfaces being rounded at the soap blank receiving edge and tapering divergently from the soap blank receiving edge. The apparatus also includes means for forcing a soap blank through the opening with the cut ends of the soap blank simultaneously contacting the end die surfaces of the opening thereby subjecting the cut ends of each soap blank to shear and normal stresses.

The invention also comprises a method for end-shaping blanks of soap or the like cut from extruded logs preliminary to die box pressing the soap blanks which includes the step of subjecting the cut ends of a soap blank to shear and normal stresses by forcing the soap blank through an opening defined by spaced apart die surfaces such that the cut ends of the soap blank simultaneously contact the spaced apart die surfaces, the spaced apart die surfaces being separated by less than the longitudinal length of the soap blank, being rounded at the soap blank receiving edge and tapering divergently from the soap blank receiving edge.

DESCRIPTION OF THE DRAWINGS For a more complete understanding of the invention reference is made to the accompanying drawing in which:

FIG. 1 is a plan view of the apparatus of this invention including an embodiment of a reworking die in section.

FIG. 2 is a side elevation view of the apparatus of this invention including an embodiment of a reworking die.

FIG. 3 is an enlarged fragmentary cross-sectional view showing the operation of the reworking die.

FIG. 4 is similar to FIG. 3 showing a later stage of the operation.

3 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 the reference numeral 5 indicates the rigid blunt reworking die used to rework the surfaces of severance on the blanks 1.

In its simplest form, namely single blank processing, the apparatus of this invention consists of an extruder 6 which forms the plastic material into a log 7 on the conveyor belt 2. The conveyor belt 2 transports the log of plastic material 7 in the direction of the axis of extrusion to the blank cutter 8. The blank cutter 8 severs the log 7 into blanks 1 approximately the size of the finished product. It is during this cutting process that the laminar flow lines in the blanks 1 are exposed and opened.

The blanks 1 then proceed on the conveyor belt until they reach the stop 3. When a blank 1 has been properly aligned by the stop 3, pusher bar 4 presses the blank 1 through the reworking die 5. The blank 1 is sized about two to six sixteenths of an inch in length greater than the minimum opening between the die surfaces 9 and 9' for proper bending of the flow lines, and stop 3 is aligned such that there is an overage of one to three sixteenths of an inch at each end of the blank 1 with respect to the opening of die 5. As the blank enters the reworking die, high normal forces created by the leading rounded surfaces 9 and 9' (see FIGS. 3 and 4) force the flow lines in the blank to bend perpendicularly and to be compressed. Typically for ordinary size soap bars, the radius of curvature of rounded surface 9 is from one-eighth to onefourth inch. From rounded surfaces 9, the die surfaces diverge, typically at an angle of about 10. Hence after the blank passes the leading rounded surface 9 of the die, the increased cross-sectional area relieves the pressure on the blank. In this description the reworking die has been used as a preformer and the blank soap bar might now proceed to further processing as to die box 10. Had the reworking die been an integral part of the press die box, the soap blank, after passing through the die, would immediately enter the die box for stamping.

The alternate method wherein the soap log is used rather than the blanks would function in a similar manner. However, there would be no cutter and the die itself would be used simultaneously to sever and rework the blanks.

As is well known in the art, the soap must have the proper plasticity and be in the proper temperature range (normal for good plodding characteristics 32 F .to

'F.) for the reworking die to operate well. The lower the temperature the harder the soap hence spreading of the flow lines occurs and not smearing. In the high temperature range the soap will tend to melt and flow the soap over the end flow lines and this again does not produce the desired effect of bending the flow lines.

It will be understood that the reworking device can be modified considerably without departing from the invention. For example the number of reworking dies may be increased to provide a higher processing rate and the shape and size of the die may be modified in accordance with the shape of the product to be processed.

Accordingly, it should be understood that the above described form of the invention should be considered as illustrative only and not as limiting the scope of the following claim.

We claim:

1. Method for end-shaping blanks of soap cut from extruded logs preliminary to die box pressing said soap blanks which comprises subjecting the cut ends of a soap blank to shear and normal stresses by forcing the soap blank through an opening defined by spaced apart rigid die surfaces such that the cut ends of the soap blank simultaneously contact the spaced apart die surfaces, the spaced apart dies surfaces being rounded at the soap blank receiving edge and tapering divergently from the soap blank receiving edge, the rounded soap blank receiving edges being separated by a distance of about two-sixteenths to six-sixteenths of an inch less than the distance between the cut ends of the soap blank.

References Cited UNITED STATES PATENTS 2,713,188 7/1955 Garvey 258 ROBERT F. WHITE, Primary Examiner W. E. HOAG, Assistant Examiner US. Cl. X.R. 264-294 

